Radio transmission and reception is the technology of using radio waves to carry information, such as sound, by systematically modulating properties of electromagnetic energy waves transmitted through space, such as their amplitude, frequency, phase, or pulse width. When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form.
Radio systems need a transmitter to modulate (change) some property of the energy produced to impress a signal on it, for example using amplitude modulation or angle modulation (which can be frequency modulation or phase modulation). Radio systems also need an antenna to convert electric currents into radio waves, and vice versa. An antenna can be used for both transmitting and receiving. The electrical resonance of tuned circuits in radios allows individual stations to be selected or certain frequencies (channels) to be monitored. The electromagnetic wave is intercepted by a tuned receiving antenna. A radio receiver receives its input from an antenna and converts it into a form that is usable for the consumer, such as sound, pictures, digital data, measurement values, navigational positions, etc. Radio frequencies occupy the frequency range from 3 kHz to 300 GHz, although commercially important uses of radio use only a small part of this spectrum.
A radio communication system sends signals by radio. The radio equipment involved in communication systems includes a transmitter and a receiver, each having an antenna and appropriate terminal equipment such as a microphone at the transmitter and a speaker at the receiver, in the case of a voice-communication system.
Some communication systems contain two radios that are connected to a central headset/microphone and are powered by a centralized power supply and a communication controller (used to control the system) and typically configured as a closed-loop system. These systems generally contain Push-To-Talk (PTT) devices which can introduce communication noise generated by the configuration of the system and the circuitry in the devices.